Question: The arithmetic sequence $(a_i)$ is defined by the formula: $a_i = -1 + 4(i - 1)$ What is $a_{4}$, the fourth term in the sequence?
Solution: From the given formula, we can see that the first term of the sequence is $-1$ and the common difference is $4$ To find $a_{4}$ , we can simply substitute $i = 4$ into the given formula. Therefore, the fourth term is equal to $a_{4} = -1 + 4 (4 - 1) = 11$.